This invention relates to a system for allowing several different wireless telecommunications service providers to co-locate multiple dual polarization antenna panels on a common monopole or lattice-type tower, reducing the number of such towers needed to service a given market area. More particularly, the system allows for each service provider to independently adjust their respective antenna panels for optimal signal transmission and reception without interfering with the antenna panels of the other co-located service providers. The antenna panels are arranged in a small-footprint stackable configuration, designed to minimizing back lobe emissions and improving the overall visual appearance of the tower or pole.
With the recent growth of wireless cellular communication systems, many telecommunications service providers are constructing proprietary networks of cellular antenna sites spaced optimally over their service areas so as to provide continuous coverage for their subscribers. Each of these sites typically includes a monopole or lattice-type tower rising up to 175 feet above ground level, enclosures and equipment boxes housing radio, telephone and power connections, and perimeter security fencing. A Typical prior art transceiver antenna tower is shown generally in FIG. 1.
Optimal spacing of transceiver sites is dependent upon several factors including the type of service provided, nearby geographic features which may block signals (hills, tall buildings, etc.), the type of equipment used, and the amount of communications traffic handled by the site. Of course with proprietary systems, if two or more wireless service providers compete in the same market area, each requires their own network of transceiver sites, generally doubling the number of towers required to optimally service the area.
With the advent of personal communication systems (PCS), there will be a significant increase in the number of transceiver sites located in each market area. The operating frequencies of PCS, between 1850 and 1990 MHz, require two to four transceiver sites to cover the same area currently serviced by a single cellular transceiver site. Additionally, it is expected that each market area will be serviced by two to four times as many PCS providers as it is currently by cellular service providers. Clearly, if each PCS provider establishes a proprietary PCS transceiver network, the number of transceiver sites in a community will increase significantly.
Communities often strongly object to the initial installation or subsequent installation of additional transceiver sites because of the ungainly visual appearance of the current tower and antenna designs. With many conventional cellular transceiver sites, the tower is either a lattice-type tower constructed of steel angles and braces, or in the more recent sites, a monopole tower. The monopole tower designs are currently more favored, as they are easier to erect, and have a less objectionable appearance than the lattice-type towers. However, regardless of the type of tower used, one type of conventional antenna used with such towers may consist of six or more flat panel antennas employing three pairs of panels in a spatial diversity receive configuration. Each spatial diversity receive pair is located on the outer end of horizontally aligned elongated arms such that the antenna panels are mounted or spaced in a triangular array. Three or more transmit antenna panels are then mounted in a more closely packed triangular array adjacent the upper end of the tower and central to the spatial diversity receive array, such as is shown in FIG. 3.
Heretofore, spatial diversity receive antenna technology requires individual antenna panels to be separated by several feet for optimal signal reception, and requires the supporting framework to be fairly large. It is known that this large antenna separation allows undesired radio frequency energy emissions, known as side and back lobe emissions, to propagate out from the sides and rear of each antenna panel. Side and back lobe emissions cause deterioration in the overall performance of the transceiver site by interfering with the desired front lobe emissions of the surrounding antenna panels. Additionally, these large and ungainly horizontal antenna support frames contribute significantly to the perceived unattractiveness of transceiver sites, and are the source of many complaints raised by citizens at community zoning meetings held prior to zoning approval for transceiver sites.
It has been a long-standing objective of cellular and PCS service providers to allay community concerns by enhancing the visual appearance of transceiver sites and reducing the number of sites required to service a given area. A dramatic reduction in the number of transceiver sites can be obtained through co-location, i.e. allowing multiple wireless service providers to locate their antenna equipment on a common tower at a single transceiver site. The actual reduction in the number of transceiver sites realized through co-location is dependent on the number of different service providers' antenna arrays which may be placed on the common tower.
The maximum number of antenna panels which may be placed on any given tower is oftentimes limited by that particular tower's maximum wind loading capability. Wind loading capability is a measure of the structural strength of the tower, and is determined by its size and construction, applicable building codes and regulations, and the type of antenna array the tower was designed to support. Since many cellular and PCS service providers have designed proprietary transceiver sites, their towers were designed to only carry their own antenna arrays. Correspondingly, due to the structural design and wind load features of horizontal antenna frames, the number of such antenna arrays which can be co-located onto the existing towers at each transceiver site is limited.